Is Kate Upton Dating Mark Sanchez?

Does Kate Upton have a sports star boyfriend to go along with her Sports Illustrated swimsuit issue cover?

Well, it's complicated. The stunning blonde, 19, has been linked to New York Jets quarterback Mark Sanchez for months -- but neither Upton nor Sanchez, 25, have confirmed their relationship.

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"She says they are friends," an insider tells Us Weekly, adding that they met through her older sister, who works for the Jets. "They started hanging out about 7 months ago."

Adds the source of Sanchez: "He is always at her apartment [and] has dropped off gifts and flowers for her . . . It isn't serious."

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Upton remained coy about the rumors when TMZ asked about their status. "I don't know," she said Tuesday. "It's whatever you think!"

For his part, Sanchez dated actress Jamie-Lynn Sigler back in 2010.

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Says a Sanchez source: "Mark and Kate Upton are friends and he thinks its great that she is having so much success."